In semiconductor manufacturing, as the size of silicon wafers increases and the size of semiconductor devices decreases, there is an ever greater need for the application of uniform thin films to the silicon wafers. However, the uniformity of a thin film is strongly dependent upon precise pressure control of the gases within the semiconductor manufacturing equipment.
Pendulum valves have been used in high-purity gas delivery systems required for semiconductor manufacturing and other thin film coating processes. Pendulum valves are often used to control the pressure in high-vacuum chambers (e.g., a pressure on the order of one torr or less) and are typically located between the vacuum chamber and a turbo pump. In pendulum valve 100, a valve body can typically move from a fully closed position to a fully open position. This generally involves rotating the valve body from the open position to a position that is aligned with the gas flow channel through the valve and then linearly moving the valve body to the fully closed position, thus sealing the valve.
Prior art pendulum valves typically use a step motor to provide rotational movement to the valve body and pneumatics to provide linear movement to the valve body. However, these prior art systems are limited because pneumatics do not provide for accurate linear positioning, and in systems using pneumatics, the valve body can usually be linearly positioned only in the fully closed position (e.g., in the sealed position) or in one partially open position ready for rotation. However, the valve body cannot be positioned over a range of continuous partially open positions to control the throttling of gas through the flow channel.
To compensate for the lack of throttling with pneumatics, one prior art valve employs a secondary valve. When the valve body of this prior art valve is in the fully closed position, fine pressure adjustments are done by opening and closing the smaller secondary port (e.g., the secondary valve). This system, however, is limited because it requires an extra valve and more valve controls to perform throttling functions. Additionally, because of the extra valves, this prior art system is difficult to manufacture, service and maintain, causing valuable chip fabrication equipment to be shut down for hours while this type of pendulum valve is serviced or maintained.
In another prior art system, the pneumatic pressure control is refined so that the valve body can be positioned in a sealed position, a center partially open position, and a partially open position. However, even with two partially open positions, these valves do not provide sufficient throttling of gas flow for thin film coating processes that require accurate and uniform control of the thin film deposition. Additionally, the pneumatics of these pendulum valves make the pendulum valves difficult to manufacture, service and maintain, again leading to hours of down time when the pendulum valve needs service or cleaning.
Another disadvantage of prior art systems is that, over time, the pressures experienced by the pendulum valve tend to bend the valve body. Because the valve body is bent, the valve body may not form a tight seal even when the valve body is moved to the fully closed position, leading to significant leakage and a general degrading of the integrity of the vacuum in the vacuum chamber. Thus, the ability of the prior art pendulum valves to create an adequate seal decreases over time as the valve bodies bend.